The present disclosure relates generally to fault condition monitoring of printed circuit assemblies, such as those utilized within a digital computer, and specifically to the detection and prevention of the catastrophic failure of the dielectric in a multilayer printed circuit assembly, including smoke and burn detection and prevention.
Modern digital computers often use an array of multilayer printed circuit boards or assemblies to hold the digital logic components, interconnect them, and provide power to them. The amount of power used in such arrays of printed circuit assemblies is very high, on the order of tens of kilowatts. If a breakdown in the printed circuit dielectric between voltage and ground occurs, sufficient power is available to cause burning (carbonization) and potential fire on the failed printed circuit assembly. Such a catastrophic failure and fire may damage other closely spaced printed circuit assemblies.
The prior art burn detection method of smoke, or combustion product, detectors suffer from unreliability and a slow response time relative to the speed of the burn. Also previously utilized, overcurrent detection in power supplies is now insufficient to protect an individual printed circuit assembly. This is because the power supply may be outputting sufficient current to allow the catastrophic burn of an individual multilayer printed circuit assembly without such sufficient excess, or overcurrent as may be detected and utilized to protect such assembly. Finally, it would be possible to fuse each individual printed circuit assembly but such fusing is often inefficient or impractical. Fuses have a voltage drop and interfere with regulation of the direct current (DC) voltage source. Fuses are physically large for the currents involved, approximately 100 amperes, and do not fit on a printed circuit board. Furthermore, if an individual printed circuit card assembly is fused at full circuit current, a burn may still occur and not blow the fuse.
One solution to the above problem includes disposing two planes of parallel copper planes separated by a thin ply of epoxy and fiberglass (e.g., prepeg) across the PCB to detect leakage current. However, this solution requires an active or power plane to be disposed very close to the sense plane increasing the risk of the power plane shorting to the sense plane. Moreover, this solution does not support ball grid array (BGA) and land grid array (LGA) technologies.
Accordingly, an improved smoke and burn detection and prevention method and apparatus is desired that supports BGA/LGA technologies.